1. Urban Water Systems10 Urban drainage© PK, 2005 – page 1 10Urban Drainage 10.1 Rain characterisation 10.2 Rain-runoff process 10.3 Sewer structure elements 10.4 Stormwater concepts Technische Universität Dresden Department of Hydro Science, Institute for Urban Water Management Peter Krebs Urban Water Systems

2. 10 Urban drainage© PK, 2005 – page 2 10.1 Rain characterisation 10 Urban drainage

3. Urban Water Systems10 Urban drainage© PK, 2005 – page 3 Rain-runoff process Rain  Runoff Not predictable Can be analysed statistically Affected by systematic changes Cannot be analysed statistically Models Measurements Dimensioning

4. Urban Water Systems10 Urban drainage© PK, 2005 – page 4 Stormwater runoff  decisive for pipe diameter WWTP operation is disturbed for longer than the rain duration Significance of stormwater Contaminated after surface runoff Erosion of sewer sediments Sewage overflow due to stormwater runoff

5. Urban Water Systems10 Urban drainage© PK, 2005 – page 5 Rain measurement SyphonWeighingTipping bucket

6. Urban Water Systems10 Urban drainage© PK, 2005 – page 6 Description of rain events From Dyck and Peschke (1989) Long duration event Intense event

7. Urban Water Systems10 Urban drainage© PK, 2005 – page 7 Rain measurement Defined opening area of 200 cm 2 Normalised shape in vertical section Measurement error depending on Wind velocity field Rain or snow Wind protection shield

8. Urban Water Systems10 Urban drainage© PK, 2005 – page 8 Description of rain (precipitation) Rain height h R in mm Rain duration t R in min Rain intensity in mm/min, l/(s·ha),  m/s Rain intensity Time t tRtR r Area = h R Block rain

9. Urban Water Systems10 Urban drainage© PK, 2005 – page 9 Resolution in time Time (min) r (l/(s·ha))

10. Urban Water Systems10 Urban drainage© PK, 2005 – page 10 Resolution in time  Runoff

11. Urban Water Systems10 Urban drainage© PK, 2005 – page 11 Resolution in time  retention volume Date of rain event Retention volume in m 3  t = 5 min  t = 10 min 29.08.1964 07.07.1965 17.07.1963 19.05.1964 1890 1792 1232 1089 1886 1772 1225 1075 From Krejci et al. (1994)

12. Urban Water Systems10 Urban drainage© PK, 2005 – page 12 Resolution in space

13. Urban Water Systems10 Urban drainage© PK, 2005 – page 13 Assignment of rain gauges to sub-catchments Thiessen-Polygon (from Dracos, 1980)

14. Urban Water Systems10 Urban drainage© PK, 2005 – page 14 Extreme value frequency (Reinhold, 1940)

15. Urban Water Systems10 Urban drainage© PK, 2005 – page 15 Reference rain intensity r 15(1) in l/(s·ha) Baden-Baden 120 Berlin 94 Bonn 108 Bremen 108 Dortmund 120 Dresden 102 Essen 96 Flensburg 100 Frankfurt/Main 120 Garmisch-Patenkirchen 200 Göttingen 98 Hamburg 99 Hannover 100 Köln 97 Konstanz 150 Krefeld 112 Lübeck 106 Mainz 117 München 135 Münster 100 Oldenburg 108 Osnabrück 150 Passau 123 Saarland 135 Stuttgart 126 Tübingen 200 Ulm (Donau) 140 Wetzlar 122 Wilhelmshaven 85 Wolfsburg 112

16. Urban Water Systems10 Urban drainage© PK, 2005 – page 16 Frequency analysis z-years event

17. Urban Water Systems10 Urban drainage© PK, 2005 – page 17 Frequency analysis z-years event Mean value Standard deviation Frequency factor f K = f (duration of data collection, frequency)  from tables

18. Urban Water Systems10 Urban drainage© PK, 2005 – page 18 Return period for sewer design Return period (a)Catchment Mixed structures City centre, important industry area Streets, not in cities areas Street underpass, underground 1 – 2 1 – 5 1 5 – 20

19. Urban Water Systems10 Urban drainage© PK, 2005 – page 19 Historical rain events Significance Critical impacts to receiving waters Less significance for sewer design Prerequisites for data collection Measuring time period Resolution in time Resolution in space Time synchronisation Data bank systems

20. Urban Water Systems10 Urban drainage© PK, 2005 – page 20 10.2 Rain-runoff process 10 Urban drainage

21. Urban Water Systems10 Urban drainage© PK, 2005 – page 21 Peak runoff factor Runoff duration Rain duration r·Ar·A QRQR r max ·A QPQP

22. Urban Water Systems10 Urban drainage© PK, 2005 – page 22 Peak runoff factor  P and coefficient  P Surface material PP Housing density PP Metal and Stone roof0,95 Class I 350 Inh/ha 0,8 Roofing tile and felt0,90 Flat roof0,50 – 0,70 Class II 250 Inh/ha 0,60 – 0,65 Asphalt road0,85 – 0,90 Rough road surface0,75 – 0,85 Class III 150 Inh/ha 0,40 – 0,52 Gravel road0,25 – 0,60 Gravel path0,15 – 0,30 Class IV 100 Inh/ha 0,25 – 0,46 Unpaved area0,10 – 0,20 Park and Garden0,05 – 0,10 Class V no housing 0,05 – 0,35 Meadow, Forest0

23. Urban Water Systems10 Urban drainage© PK, 2005 – page 23 Peak runoff factor = f(rain intensity r, slope J) 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 00,20,40,60,81 Impervious area (-) Peak runoff factor  P (-) r = 225 (l/(s·ha)) r = 180 (l/(s·ha)) r = 130 (l/(s·ha)) r = 100 (l/(s·ha)) 4% < J < 10%

24. Urban Water Systems10 Urban drainage© PK, 2005 – page 24 Dry- and wet-weather runoff Population densitye = 100 Inh/ha DrWa-consumption Rain intensity Peak runoff factor q = 100 l/(Inh·d) r 15(1) = 100 l/(s·ha)  P = 0,4 DW WW

25. Urban Water Systems10 Urban drainage© PK, 2005 – page 25 Rain-runoff-process in two steps Runoff production Runoff concentration Time r·AQr·AQ

26. Urban Water Systems10 Urban drainage© PK, 2005 – page 26 Losses and runoff production Permanent losses Infiltration losses Depression storage Runoff Wetting losses Rain duration Rain intensity

27. Urban Water Systems10 Urban drainage© PK, 2005 – page 27 Pervious area

28. Urban Water Systems10 Urban drainage© PK, 2005 – page 28 Surface runoff and infiltration

29. Urban Water Systems10 Urban drainage© PK, 2005 – page 29 Surface classification

30. Urban Water Systems10 Urban drainage© PK, 2005 – page 30 tRtR tCtC rara t R < t C tCtC rbrb t R = t C 2 t C Rain duration to produce maximum runoff A QaQa QbQb

31. Urban Water Systems10 Urban drainage© PK, 2005 – page 31 tRtR rcrc t R > t C tR+tCtR+tC A Concentration time = surface runoff time + flow time in sewer QcQc Rain duration to produce maximum runoff

32. Urban Water Systems10 Urban drainage© PK, 2005 – page 32 Assumption of decisive rain duration with a lack of information ClassSloppeImpervious fractiontRtR 1< 1%  50% 15 min 12341234 < 1% 1% - 4% 4% - 10% > 10% > 50%  50% 10 min 4> 10%> 50%5 min

33. Urban Water Systems10 Urban drainage© PK, 2005 – page 33 Rationale method 3 4562 1 Iteration with effective concentration time t C for Point 3 for Point 4

34. Urban Water Systems10 Urban drainage© PK, 2005 – page 34 Rationale method Section123456Comments L reach (m)12018060180 v (m/s) Flow time (min) t R = t sur + t flo (min)t A = 5 min r (t R, z) (l/(s·ha)) (Reinhold, 1940) A i (ha)2313  P (-) 0,40,6 0,5 A red,i (ha)  A red,i (ha) Q Rain (m 3 /s) Q Rain = r·  A red,i const. Q (m 3 /s) Q Rain,tot (m 3 /s) Q DW (m 3 /s) Q m (m 3 /s)

35. Urban Water Systems10 Urban drainage© PK, 2005 – page 35 Application of rain-runoff models Rationale method Detailed numerical simulationen  Maximum flow rate  Extreme rain event as input  Dimensioning of sewer cross section  Flow as a function of time at every point in the system  Measured rain events as input  Evaluation of functionality of sewer system  Optimisation of operation and control  Estimation of impact to receiving water

36. Urban Water Systems10 Urban drainage© PK, 2005 – page 36 10.3 Sewer structure elements 10 Urban drainage

37. Urban Water Systems10 Urban drainage© PK, 2005 – page 37 Groundwater, Drainage, … Rain water CSOWWTP Domestic and industrial sewage  clean polluted Comb syst Groundwater, Drainage, … Rain water CSOWWTP Domestic and industrial sewage  clean polluted Comb syst Infiltration Groundwater aquifer Combined system

38. Urban Water Systems10 Urban drainage© PK, 2005 – page 38 Combined system

39. Urban Water Systems10 Urban drainage© PK, 2005 – page 39 (DIN 1998) No access for rehabilitation Combined system Cross section through street underground Gully Manhole House connection

40. Urban Water Systems10 Urban drainage© PK, 2005 – page 40 Separate system Groundwater, drainage, … Rain water Storm sewer WWTP Domestic and industrial sewage  clean polluted Sewage sewer Rainwater treatment Groundwater, drainage, … Rain water Storm sewer WWTP Domestic and industrial sewage  clean polluted Sewage sewer Infiltration Groundwater aquifer Rainwater treatment

41. Urban Water Systems10 Urban drainage© PK, 2005 – page 41 Separate system

42. Urban Water Systems10 Urban drainage© PK, 2005 – page 42 DIN (1998) Separate system Cross section through street underground Gully Manholes House connection: sewage Street water Roof water

43. Urban Water Systems10 Urban drainage© PK, 2005 – page 43 Comparison of combined and separate system TargetCombined systemSeparate system Distinct load variationWWTP Receiving water Sewer system Storage tanks needed Increased design requirements Theoretically relatively homogeneous loading re. both flow and load CSO includes part of the sewage Time delay before combined water is discharged Stormwater discharge untreated No sewage directly to river No retention, quicker discharge Lower contruction costs Space requirements in the region of retention tanks 2 sewers, more expensive More space requirement in the ground Not retention tanks needed

44. Urban Water Systems10 Urban drainage© PK, 2005 – page 44 TargetCombined systemSeparate system Frequent self-flushingSediments Maintenance House connection Rel. small slope needed More susceptible to sedimentation Less cleaning required Better air exchange More cleaning required Increased total sewer length No mis-connections Backwater effect to cellars Mis-connections No backwater effects Pumping Higher slope needed High pumping performance needed which is used only seldomly If possible only sewage has to be pumped Comparison of combined and separate system

45. Urban Water Systems10 Urban drainage© PK, 2005 – page 45 Sewer cross sections

46. Urban Water Systems10 Urban drainage© PK, 2005 – page 46 „Other“ sewer profile

47. Urban Water Systems10 Urban drainage© PK, 2005 – page 47 Elements of stormwater treatment FunctionElementApplied in CSO structureOverflow Combined water retention Stormwater treatment Sewer overflow Combined system First flush tank Flow-through tank Pollutants retention Sewage retention tank Combined tank Storage channel Combined system Separate system Stormwater retentionComb., sep. system Gully Upstream comb. Syst. Comb., sep. system

48. Urban Water Systems10 Urban drainage© PK, 2005 – page 48 Operation of combined water oberflow structures River CWRT combined water retention tank WWTP wastewater treatment plant SO sewer overflow CSO CSO structure CSO WWTP CWRTR Weak rain CSO moderate rain CSO rain intense CSO event Extreme- SO CWRTR WWTP

49. Urban Water Systems10 Urban drainage© PK, 2005 – page 49 Overflow structure with side weir Overflow at Throttle flow Mixing ratio resp. with c DW > 600 mg/l

50. Urban Water Systems10 Urban drainage© PK, 2005 – page 50 „Leaping Weir“, bottom outlet

51. Urban Water Systems10 Urban drainage© PK, 2005 – page 51 Combined water retention tank First flush tank Flow-through tank Combined tank First flush characteristics Short concentration time (< 15 min) Moderate slope Continuous settling of suspended solids Combination of first-flush storage and settling part

52. Urban Water Systems10 Urban drainage© PK, 2005 – page 52 First flush tank WWTP SO CSO WWTP SO, CSO Off-lineIn-line Emptying with pump Separate flow to WWTP Emptying through slope Flow to WWTP through tank Total stored volume is directed to WWTP!

53. Urban Water Systems10 Urban drainage© PK, 2005 – page 53 Flow-through tank Off-lineIn-line Emptying with pump Separate flow to WWTP Emptying though slope Flow to WWTP through tank Sugnificant part of overflow flows through tank! WWTP SO CSO WWTP SO, CSO

54. Urban Water Systems10 Urban drainage© PK, 2005 – page 54 Storage channel overflow Manhole

55. Urban Water Systems10 Urban drainage© PK, 2005 – page 55 Dimensioning of CWRT (ATV A128) Goal for annual COD load „Overflow + WWTP effluent  Storm water load“ SF o + SF WWTP  SF St c COD concentration e 0 annual overflow rate mit c DW : c St : c WWTP = 600 : 107 : 70 m mixing ratio

56. Urban Water Systems10 Urban drainage© PK, 2005 – page 56 Specific retention volume and overflow rate Specific stormwater runoff to WWTP q St (l/(s·ha*red)) Specific storage volume V Sp (m 3 /ha red )

57. Urban Water Systems10 Urban drainage© PK, 2005 – page 57 Weir Baffle Weir CSOFirst-flush tankThrottle Pump First-flush tank ThrottleCSO Baffle Weir CSO Weir to first flush tank emptying First flush tank off-line Section Top view

58. Urban Water Systems10 Urban drainage© PK, 2005 – page 58 First-flush tank Baffle Weir CSO Throttle Dry-weather flume CSO Weir Baffle First-flush tank in-line First-flush tank Throttle Cross section Longitudinal section Top view

59. Urban Water Systems10 Urban drainage© PK, 2005 – page 59 Flow-through tank off-line Section I Section II Top view Effluent weir Flow-through tank Pump Baffle Weir CSO Weir to flow- through tank emptying Throttle Weir CSO BaffleWeir to tank Throttle Flow-through tank Cleaning device Effluent weir

60. Urban Water Systems10 Urban drainage© PK, 2005 – page 60 Flow-through tank in-line Section Top view Flow-through tank Throttle Cleaning device Effluent weir Baffle Weir CSO emptying Baffle Weir CSO Cleaning device Effluent to receiving water

61. Urban Water Systems10 Urban drainage© PK, 2005 – page 61 Combined tank off-line Section Baffle Weir CSO Flow-through tank First-flush tank Pump Top view emptying Weir to first-flush tank Weir to flow-through tank Baffle Baffle Weir CSO Weir to FFTWeir to FTT Flow-through tank First-flush tank Throttle Baffle Effluent weir

62. Urban Water Systems10 Urban drainage© PK, 2005 – page 62 Circular tank in-line Section Top view Baffle Weir CSO emptying Throttle Dry-weather flow Baffle Weir CSO

63. Urban Water Systems10 Urban drainage© PK, 2005 – page 63 Cleaning device

64. Urban Water Systems10 Urban drainage© PK, 2005 – page 64 Design of stormwater retention tank Estimation with rectangular rain graph Intensity Return period z = 5 a Impervious areaA red = 3 ha Duration t N = ?? Inflow volume Outflow volume Storage volume

65. Urban Water Systems10 Urban drainage© PK, 2005 – page 65 Design of stormwater retention tank 0 100 200 300 400 500 600 700 800 0102030405060 Rain duration t R (min) Water volume (m 3 ) 0 50 100 150 200 250 300 350 Rain intensity r (l/(s·ha)) Inflow volume Outflow volume Retention volume Rain intensity

66. Urban Water Systems10 Urban drainage© PK, 2005 – page 66 Decentralised stormwater retention Green roof, flat gravel roof Biotope Retention channel Parking lot as a retention area Stormwater use

67. Urban Water Systems10 Urban drainage© PK, 2005 – page 67 Sewage retention tank Overflow Receiving water CSO Combined water retention WWTP WWTP effluent Sewage retention tank

68. Urban Water Systems10 Urban drainage© PK, 2005 – page 68  CSO without retention —— combined water retention tank ------ Sewage retention tank Effects of combined water an sewage retention tank Long event with rel. low intensity Short event with moderate intensity 0 1 2 3 4 7:007:157:307:458:008:158:30 N-load (gN/s) Event 13  CSO —— CWRT ------ SRT

69. Urban Water Systems10 Urban drainage© PK, 2005 – page 69 0 1 2 3 4 2:503:203:504:204:505:20 N-load (gN/s) Event 11 Short event with high intensity  Acute reveiving water impact is reduced at short events with moderate intensity  WWTP load is reduced during critical phase for N-Elimination Combined water retention tank Sewage retention tank Effects of combined water an sewage retention tank  CSO without retention —— combined water retention tank ------ Sewage retention tank

70. Urban Water Systems10 Urban drainage© PK, 2005 – page 70 Retention of solid matter Gully pot Related catchment app. 200 m 3 Withdrawal zone Sediment zone, largely variable Water depth 80 – 100 cm Volume 280 – 380 l

71. Urban Water Systems10 Urban drainage© PK, 2005 – page 71 Stormwater infiltration Means Conditions Effects Establish pervious and semi-pervious surfaces Collecting e.g. roof water in infiltration devices Land use of sub-catchment Composition of soil Distance to drinking water extraction Reduction of runoff Reduction of loads in CSOs Increase of groundwater recharge (small)

72. Urban Water Systems10 Urban drainage© PK, 2005 – page 72 Optimum range for infiltration 10 -10 10 -8 10 -6 10 -4 10 -2 1 Gravel Fine gravel Sandy gravel Coarse sand Sand Fine sand Loamy sand Loam Clayey loam Clay  High infiltration capacityHigh sorption capacity 

73. Urban Water Systems10 Urban drainage© PK, 2005 – page 73 Trough infiltration Upper layer with low permeability lower layer with high permeability Bank protection Frost protection Filter layer, sand, h = 50 cm Humus, h = 30 cm ev. overflow Max. water level Maximum groundwater level min. 1 m

74. Urban Water Systems10 Urban drainage© PK, 2005 – page 74 Infiltration pipe

75. Urban Water Systems10 Urban drainage© PK, 2005 – page 75 Infiltration shaft

76. Urban Water Systems10 Urban drainage© PK, 2005 – page 76 Trough-trench system

77. Urban Water Systems10 Urban drainage© PK, 2005 – page 77 Trough-trench system

78. Urban Water Systems10 Urban drainage© PK, 2005 – page 78 Trough-trench syestem Sieker (2001)

79. Urban Water Systems10 Urban drainage© PK, 2005 – page 79 vortex drop shaft

80. Urban Water Systems10 Urban drainage© PK, 2005 – page 80 outflow inflow 10m Dry-weather pipe Wet-weather pipe flushing Low passage, change to pressurised flow

81. Urban Water Systems10 Urban drainage© PK, 2005 – page 81 House connection, sparate system private  public sewage stormwater

82. Urban Water Systems10 Urban drainage© PK, 2005 – page 82 „vacuum“ drainage Connection density Branch length (m) Length of total network (P/m)DN 65DN 80DN 100DN 125 0.04 – 0.06200 m800 m1000 m < 5000 m 0.06 – 0.12150 m650 m900 m300 m< 4000 m 0.12 – 0.20100 m300 m 800 m< 3000 m WWTP Vacuum station Main collector

83. Urban Water Systems10 Urban drainage© PK, 2005 – page 83 10.4 Stormwater concepts 10 Urban drainage

84. Urban Water Systems10 Urban drainage© PK, 2005 – page 84 Stormwater retention; green roof

85. Urban Water Systems10 Urban drainage© PK, 2005 – page 85 Biotope for stormwater retention

86. Urban Water Systems10 Urban drainage© PK, 2005 – page 86 Infiltration

87. Urban Water Systems10 Urban drainage© PK, 2005 – page 87 Stormwater runoff at surface

88. Urban Water Systems10 Urban drainage© PK, 2005 – page 88 Retention and infiltration pond

89. Urban Water Systems10 Urban drainage© PK, 2005 – page 89 Stormwater use